You shoot him till he dies. but if you want detailed instructions here you are:either use dinamite arrows or use dinatmite to hurt him. then after a while he will go up on a somthin and he will throw large dinamite packs. use quickdraw while the big one is near the pedastals. then after both pedastals r down. shoot the dinamite packs near the ceiling of him to lay down the kill.

You can't kill by shooting him, what you need to do is on the first part you need to use is your Loco Bow which shoots dynamite. (There is an arrowpack that lays to the left of the place you come in at) I would suggest running backwards around the outside of the rocks and timing your bow shots so that he runs into the green geysers as they explode.

For the second half get between 2 rocks (so only your head shows) on the outside. If your facing Macgruder it will be towards the left. This place made it so that I could snipe Macgruder with the rifle (One headshot makes him throw his dynamite pack). Remember to use Quickdraw to shoot the dynamite, it's the easiest way.

Also there are 2 guys that keep respawning when Macgruder is on the ledge so watch out for them and remember to collect the flasks and rifle ammo so that you don't run low and die.